1. Field of the Disclosure
This disclosure for apparatus and methods for a data processing computer to receive and process information relevant to testing whether a particular piece of equipment (a network protector) located at a remote location is operating in accordance with a set of control system rules to open and close the network protector. (See for example Class 702, subclasses 183 and 286).
2. Description of the Prior Art & Problems with Prior Art Solutions
The prior art has evolved a series of solutions to address the needs to distribute electrical power. The solutions include the use of low voltage grid or spot networks. FIG. 1 is taken from U.S. Pat. No. 4,293,886 for Network Protector Relay where the components were introduced as follows “A typical application for a network protector relay of the type disclosed herein is shown in FIG. 1. In FIG. 1 a first substation feeder 10 is connected to a primary winding 12 of a first step down transformer 14 through a three phase primary breaker 16. A secondary winding 18 of the transformer 14 is connected to a network bus 20 through a set of main contacts 22 and a first set of fuses 26 of a network protector 25. The operation of the contacts 22 is controlled by a network protector relay 24. Similarly, a second substation feeder 28 is connected to the network bus 20 through a second three phase primary breaker 30, a second step down transformer 32, a set of main contacts 34 of a second network protector 37 whose operation is controlled by a network protector relay 36, and a second set of fuses 38. The network bus 20 supplies power to a load 40. Since network protectors are often located in relatively inaccessible locations, such as in a vault beneath a street, it is desirable that the sets of contacts 22 and 34 controlled by the network protector relays 24 and 36, respectively, automatically connect and disconnect the substation feeders 10 and 28 to the network bus 20.”
A complication not shown in FIG. 1 is that the cables shown for the three phases of network bus 20 extend for distances in the range of 1000 feet or more horizontally plus vertical distances with virtually all of this extended bus hidden from view in cable runs. The network bus is apt to have several different transformers connected to the bus as opposed to the two shown here. By feeding network bus 20 with a number of different transformers, customers are provided with uninterrupted power as transformers are added or removed from the network bus 20 to correspond with the variations in power needs or other distribution issues (such as the need to compensate for a disabled component).
One of skill in the art will recognize that the load 40 connected to the network bus 20 is not a single load but rather an aggregation of many loads, possibly from a mix of industrial, commercial and residential customers. Some customers may have electrical service connected to less than all three phases of the network bus 20. The characteristics of the load change over the course of a day as factories close down for the night, as demands for air conditioning change throughout the day, and as residents come home to their residences. The characteristics of the load also shift over time as new equipment is connected at customer locations.
FIG. 2 illustrates another complication not shown in FIG. 1 that the cables that comprise network bus 20 are not continuous cables neatly arranged on transmission towers where they can be seen and visually traced. In urban settings, the combination of high load densities arising from large buildings, with very little space between, leads to locating electrical distribution equipment in underground vaults. In order to connect together various transformers to buses, cables run between vaults underground. In order to provide adequate capacity and redundancy, a multitude of cables run between vaults and the buses are effectively created by connecting together cable segments to form the bus. The relevance of the segments to this application is that the connecting together of segments leads to the risk that during a new construction or a major repair, that a first phase of one transformer may be connected to a bus carrying the second phase of other transformers. This is often called “rolled phases”.
Relays such as those referenced or disclosed in U.S. Pat. No. 4,293,886 are adapted to isolate the transformer and the connector feeder from the network bus 20 based on various electrical measurements used as inputs. These relays also restrict the reconnection of the electrical bus to the transformer unless various relationships exist between the voltages found on the feeder and network sides of the network protector.
To illustrate the point, a relay may prohibit reconnection across a network protector unless for each pair 204/224, 208/228, and 212/232 (See FIG. 5), there are:                matching voltage phases (i.e. the interconnect bus has no rolled phases), and        the voltage measured on each side of the network protector differs so that power will flow from feeders 10 and 28 (See FIG. 1) to network bus 20 (See FIG. 1) and not vice versa.        
While these network protector relays controlled the network protector, the useful information concerning measured conditions on either side of the network protector was not available to monitoring devices that receive information about transformers via power line carrier communication.
As discussed below in connection with FIG. 3, power line carrier is used by some information collection systems to send measurements and other information over a phase of the feeder buses 10 and 28 to a centralized location. At the centralized location, the information is pulled from the appropriate phase of the feeder bus by a coil and provided to a receiver 140 which also receives information about the operation of other distribution transformers. The receiver 140 may receive information from more than one phase of a particular feeder bus and from more than one feeder bus so that information about a range of network transformers (such as 108 and 112) which may be located at different locations and connected to different distribution networks (such as 136) may be aggregated at receiver 140. A co-pending and commonly assigned patent application addresses one way of conveying information over the power line carrier and then decoding the conveyed information. More specifically, U.S. Pat. No. 7,242,729 filed Apr. 25, 2005 for Signal Decoding Method and Apparatus provides one set of solutions for the decoding of information conveyed by power line carrier and is incorporated by reference in its entirety and set forth herein.
The prior art has not recognized the advantages nor provided a solution to obtain and transmit via power line carrier to a central receiver the measurements of the type used by network protector relays to trigger disconnections or allow reconnections of the network protectors 128 and 132. This void in the prior art has made it difficult to discern remotely whether a network protector relay is operating properly.
There are additional benefits available from using independent measurement devices so that the actions of a relay can be judged not only on conformity with a set of control system rules but also based on an independent assessment of at least some of the information provided to the relay.
In urban distribution systems, the distribution transformers are typically located in underground vaults. Because of the high voltage and close quarters, it is potentially dangerous to have operators enter the vault to obtain electrical measurements before or after a change in the state of a network protector. Even if the danger can be reduced sufficiently through protective equipment and special procedures, it is time consuming and inconvenient to dispatch an operator into the vault.
Recognizing the importance of accessing information about the electrical properties on each side of the network protector, at least one utility has gone through the expense of running a set of wires to allow for monitoring of the two sides of the network protector to an access point outside of the vault as indicated in FIG. 2 as 204. Given the number of network protectors in even a small distribution network, it is not desirable to incur the expense to run wiring from both sides of each network protector in a transformer vault to many various local monitoring locations outside of the transformer vaults.